The androgen receptor (AR) mediates the biological effects of androgens by regulating gene expression. This AR transcriptional activity is regulated by coactivators, among which c-Jun is important for its widespread role in AR-regulated gene expression and its potential role in prostate cancer progression. Cellular proliferation and invasiveness are two important AR biological effects involved in prostate cancer progression, and we have evidence suggesting that c-Jun coactivation of AR mediates both of these cellular processes. On the proliferation side, we have generated a series of prostate cancer cell lines that differ in c-Jun expression and, consequently, cellular proliferation. Interestingly, our data suggest that c-Jun coactivation supports prostate cancer cellular proliferation, but c-Jun transactivation is anti-proliferative. With respect to invasiveness, we have identified Ets Variant Gene 1 (ETV1) as an AR-regulated gene that mediates prostate cancer invasiveness. Importantly, AR induction of ETV1 expression is under c-Jun coactivation, representing the first demonstration of an important role for c-Jun coactivation in prostate cancer invasiveness. Hence, our major hypothesis is that the c-Jun coactivation function on AR mediates prostate cancer cell proliferation, while its transactivation function antagonizes proliferation. Additionally, we hypothesize that c-Jun supports prostate cancer cell invasiveness by enhancing both the expression and activity of ETV1. These hypotheses will be tested in three specific aims. In aim 1, we will analyze the coactivation function of c-Jun on AR by studying phosphorylated and non-phosphorylated c-Jun. The effect of phosphorylation will be mimicked by mutating both Ser63 and Ser73 to the negatively charged glutamic acid (Glu). We will also study the possibility of c-Jun in either phosphorylation form to be recruited with AR to androgen-regulated promoters by chromatin immunoprecipitation (ChIP) assays and to associate with AR in LNCaP cells. In aim 2, we will study the role of c-Jun in regulation of AR induction of ETV1 and of downstream ETV1 target genes in prostate cancer cells. c- Jun and AR will be studied for the ability to regulate ETV1 expression and ETV1 activity in prostate cancer cell invasiveness. In aim 3, we will characterize the mechanism of anti-proliferation by c-Jun transactivation in prostate cancer cells. We have previously provided data suggesting that transactivation function is anti-growth and coactivation is pro-growth. We will utilize a phosphorylation mimic of c-Jun to study its effect on LNCaP cellular proliferation and to determine downstream target genes that are involved in repression of proliferation. This proposed work will allow us to study the anti-proliferative activity of c-Jun in prostate cancer cells, an activity contrary to c-Jun's oncogenic action. In addition, our studies with ETV1 will provide an opportunity to examine the interaction between AR and c-Jun in regulating gene-specific expression. Prostate cancer is the second leading cause of death among men, undergoing a transition from the treatable hormone-dependent to the usually lethal hormone-refractory. The androgen receptor and regulatory factors are key factors in both stages of prostate cancer. We have identified the proto-oncoprotein c-Jun as an important regulatory protein for androgen receptor activity, and we propose here study the role of c-Jun in androgen receptor-regulated gene expression that controls the proliferation and metastasis of prostate cancer cells. [unreadable] [unreadable] [unreadable]